# #02 The Basic Structure of the Go file

**A go file has the following parts:**

- Package declaration
- Import packages
- **main()** function

**Example:**

```go
package main

import "fmt"

func main() {
  fmt.Println("Hello World!")
}
```

`package` keyword defines the package name because every program is a part of the package, In the above code, I set the package name as `main` which will indicate that this package belongs to the `main` package.

`import "fmt"` used to import package function. Multiple packages can be imported using `import ()`.

**Example:**

```go
import (
	"fmt"
	"time"
)

func main() {
	start := time.Now()
	t := time.Now()

	fmt.Println("Hello, 世界")
	elapsed := t.Sub(start)
	fmt.Printf("Time takes: %d\n", elapsed)
}
```

`func main() {}` is the entry point of Golang, According to [Golang](https://go.dev/ref/spec#Program_execution) reference  “The main package must have package name main and declare a function main that takes no arguments and returns no value.”

If I don’t write the `main()` function the code will not execute and return the output:

`runtime.main_main·f: function main is undeclared in the main package`.

`fmt.Println("Hello World!")` the “[fmt](https://pkg.go.dev/fmt)” package is the standard library of Go, fmt package has `I/O` functions such as `Printf(), Println(), Scanf()` so on. To use print, scan and other I/O function fmt package will require.